1. Field of the Invention
The present invention relates to a variable transfer rate control coding apparatus (variable bit coding apparatus) for efficiently coding signals by use of a smaller amount of codes in a digital recording apparatus, and more specifically to a coding apparatus for coding moving picture signals by controlling the transfer rate, that is, the code amount per unit time.
2. Description of the Prior Art
In the high efficiency coding of picture signals, the variable length coding technique is effective and reasonable, because a part of a picture having a small amount of picture data can be coded by use of a smaller amount of codes. In particular, in the case of the inter-picture prediction coding in unit of frame or field of moving picture, the amount of codes (often referred to as code amount simply, hereinafter) can be extremely reduced in the motion-less portion of the moving picture. Therefore, it is possible to increase the transmission and recording efficiency when the transfer rate (the code amount per unit time) are varied according to the contents of picture, on condition that the quality of the moving picture is roughly kept constant.
FIG. 1 is a block diagram showing a prior art variable transfer rate coding apparatus. In this prior art coding apparatus, the coding processing is executed twice for the same moving picture signals. That is, the first coding is executed in a temporal coding to determine a target transfer rate (a target code amount per unit time), and the second coding is executed in an actual coding.